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Teens call them ghost parties: gatherings organized on a whim -- at a house that's often not the host's.

Police say revelers at one such ghost party ransacked an opulent Southern California mansion, leaving $1 million in damages, and making off with medieval armor, designer suits and a $250,000 stuffed leopard.

That was last month. This week, Los Angeles County Sheriff's Department announced it had arrested 16 teens -- helped, in part, by photos they posted online of their late-night romp.